When a conduit--an electrical, coaxial, or fiberoptic cable, a hose, or the like--must pass through a wall it is standard to fit the wall with a guide tube of substantially larger inside diameter than the outside diameter of the conduit or conduits that will traverse it. Such a guide tube is cast into place in a concrete wall with its ends projecting from the respective faces of the wall. After the conduit is snaked through the tube it is necessary to provide a tight seal between the tube and the conduit. Such a seal is typically needed to act as a fire stop, that is to prevent a fire on one side of the wall from propagating through the guide tube to the other side of the wall.
Recourse has thus been had to shrink sleeves that are fitted over the guide tube and cable and then heated so that they shrink tightly into place, forming a very good seal. Such seals are typically delivered in stretched condition mounted on a coil that holds them open and that is used to install them. Once in place the support coil is screwed out and then the sleeve is heated, normally by application of hot air, for the final installation.
A problem with this system is that the shrink sleeve must be threaded over the tube and conduit, so that it is virtually impossible to avoid getting dirt and other foreign matter inside the sleeve, which foreign matter is spread around as the coil is withdrawn. The coil itself presents a disposal problem, and such a sleeve cannot normally conform tightly to longitudinally grooved or ribbed conduits. During installation of the conduit through the unshrunk assembly it is possible for the conduit to catch or hang up on the support coil, and when the coil is removed helical ridges are left that can create a leak. Furthermore it is impossible with this system to provide a sealing agent or caulk inside the sleeve as it would be wiped off as the cable is pulled through it and when the support coil is removed, so that longitudinal grooves formed in cable insulation are not adequately sealed.